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  • 11
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    The system and hardware design of real-time fan beam scatterometer data processors (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: There are no author-identified significant results in this report.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: E80-10028 , NASA-CR-160350 , RSC-3556
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 12
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    Radar systems for a polar mission, volume 3, appendices A-D, S, T (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Success is reported in the radar monitoring of such features of sea ice as concentration, floe size, leads and other water openings, drift, topographic features such as pressure ridges and hummocks, fractures, and a qualitative indication of age and thickness. Scatterometer measurements made north of Alaska show a good correlation with a scattering coefficient with apparent thickness as deduced from ice type analysis of stereo aerial photography. Indications are that frequencies from 9 GHz upward seem to be better for sea ice radar purposes than the information gathered at 0.4 GHz by a scatterometer. Some information indicates that 1 GHz is useful, but not as useful as higher frequencies. Either form of like-polarization can be used and it appears that cross-polarization may be more useful for thickness measurement. Resolution requirements have not been fully established, but most of the systems in use have had poorer resolution than 20 meters. The radar return from sea ice is found to be much different than that from lake ice. Methods to decrease side lobe levels of the Fresnel zone-plate processor and to decrease the memory requirements of a synthetic radar processor are discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-156641 , RSL-TR-291-2-VOL-3
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 13
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    Skylab S-193 Radscat microwave measurements of sea surface winds (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The S-193 Radscat made extensive measurements of many sea conditions. Measurements were taken in a tropical hurricane (Ava), a tropical storm (Christine), and in portions of extratropical cyclones. Approximately 200 scans of ocean data at 105 kilometer spacings were taken during the first two Skylab missions and another 200 during the final mission when the characteristics of the measurements changed due to damage of the antenna. Backscatter with four transmit/receive polarization combinations and emissions with horizontal and vertical receive polarizations were measured. Other surface parameters investigated for correlation with the measurements included sea temperature, air/sea temperature difference, and gravity-wave spectrum. Methods were developed to correct the microwave measurements for atmospheric effects. The radiometric data were corrected accurately for clear sky and light cloud conditions only. The radiometer measurements were used to recover the surface scattering characteristics for all atmospheric conditions excluding rain. The radiometer measurements also detected the presence of rain which signaled when the scattering measurement should not be used for surface wind estimation. Regression analysis was used to determine empirically the relation between surface parameters and the microwave measurements, after correction for atmospheric effects. Results indicate a relationship approaching square-law at 50 deg between differential scattering coefficient and wind speed with horizontally polarized scattering data showing slightly more sensitivity to wind speed than vertically polarized data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: M-3 , NASA. Lyndon B. Johnson Space Center NASA Earth Resources Surv. Symp., Vol. 1-C; p 1937-1952
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 14
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    AAFE RADSCAT data reduction programs user's guide (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Theory, design and operation of the computer programs which automate the reduction of joint radiometer and scatterometer observations are presented. The programs reduce scatterometer measurements to the normalized scattering coefficient; whereas the radiometer measurements are converted into antenna temperatures. The programs are both investigator and user oriented. Supplementary parameters are provided to aid in the interpretation of the observations. A hierarchy of diagnostics is available to evaluate the operation of the instrument, the conduct of the experiments and the quality of the records. General descriptions of the programs and their data products are also presented. This document therefore serves as a user's guide to the programs and is therefore intended to serve both the experimenter and the program operator.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA-CR-144992 , CRES-TR-186-9
    Format: application/pdf
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  • 15
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    The recovery of microwave scattering parameters from scatterometric measurements with special application to the sea (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: As part of an effort to demonstrate the value of the microwave scatterometer as a remote sea wind sensor, the interaction between an arbitrarily polarized scatterometer antenna and a noncoherent distributive target was derived and applied to develop a measuring technique to recover all the scattering parameters. The results are helpful for specifying antenna polarization properties for accurate retrieval of the parameters not only for the sea but also for other distributive scenes.
    Keywords: OCEANOGRAPHY
    Type: NASA-CR-132748 , TR186-13
    Format: application/pdf
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  • 16
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    Simultaneous active and passive microwave response of the earth - The Skylab radscat experiment (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Skylab microwave radiometer-scatterometer experiment S-193 was designed to collect simultaneous information on the radiometric emission and the backscatter from the earth from orbital altitude for the first time. A primary driving force was ascertaining the response from the oceans of both active and passive systems to variations in wind, and the ability of the passive system to aid in calibrating the active system. Numerous overland applications were also explored. Preliminary results of backscatter and emission from sea and atmosphere are shown for hurricane Ava and for two flights across the Gulf of Mexico. The results tend to confirm the most recent theoretical prediction of an approximately square-law relation between scattering coefficient for horizontal polarization and windspeed, with a somewhat smaller dependence for vertical polarization. Overland measurements show that scatterometer signals at 30 deg increase and radiometer signals decrease for terrain that has recently experienced rainfall.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: International Symposium on Remote Sensing of Environment; Apr 15, 1974 - Apr 19, 1974; Ann Arbor, MI
    Format: text
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  • 17
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    A system concept for wide swath constant incident angle coverage (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The multiple beam SAR system concept is developed and shown to readily overcome the radar ambiguity constraints associated with orbital systems, thus permitting imagery over swaths much wider than 100 km. The antenna technique permits imagery at nearly constant incidence angles. When frequency scanning is used, the center angle may be programmed. The redundant use of the antenna aperture during reception results in lower transmitted power and in shorter antenna lengths in comparison with conventional designs.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: Synthetic Aperture Radar Technology Conference; Mar 08, 1978 - Mar 10, 1978; Las Cruces, NM
    Format: text
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    NASA TECHNICAL REPORTS
  • 18
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    The theory and measurement of noncoherent microwave scattering parameters (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The radar equation for incoherent scenes is derived and scattering coefficients are introduced in a systematic way to account for the complete interaction between the incident wave and the random scene. Intensity (power) and correlation techniques similar to that for coherent targets are proposed to measure all the scattering parameters. The sensitivity of the intensity technique to various practical realizations of the antenna polarization requirements is evaluated by means of computer simulated measurements, conducted with a scattering characteristic similar to that of the sea. It was shown that for scenes satisfying reciprocity one must admit three new cross-correlation scattering coefficients in addition to the commonly measured autocorrelation coefficients.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Antennas and Propagation; AP-25; Nov. 197
    Format: text
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  • 19
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    The recovery of polarized apparent temperature distributions of flat scenes from antenna temperature measurements (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The reception theory for quasi-monochromatic partially polarized emissions is employed to describe the antenna temperature when observing a flat scene from within or above an absorbing/emitting atmosphere. When the polarization aspects of the antenna and scene are carefully observed, the resulting integral expression for the antenna temperature differs significantly from that reported for polarization invariant temperature distributions. It is observed that the antenna couples to both emitted surface polarizations, and the phase character of the antenna introduces a term involving the product of the polarized and cross-polarized antenna patterns. A matrix approximation of the integral expression is suggested and developed as a means for inverting polarized antenna temperature observations for the underlying partially polarized apparent temperature distributions.
    Keywords: COMMUNICATIONS
    Type: IEEE Transactions on Antennas and Propagation; AP-22; May 1974
    Format: text
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  • 20
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    A simple formulation of oxygen absorption at centimeter wavelengths (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Carefully performed experiments by a number of investigators have supported the Van Vleck line shape theory for oxygen absorption in the lower-frequency wing (0-50 GHz). In view of the frequent need to compute oxygen absorption at centimeter wavelengths and lower a computationally simple four-line absorption model based on the Van Vleck theory is offered. The approximation yields computational accuracy better than 1% over the entire range of atmospheric pressures and temperatures for frequencies less than 30 GHz when it is compared with the Van Vleck 45-line expression. The versatility of the model in adapting to various line-broadening expressions is also shown. Instead of refining the present theories, this communication is mainly intended to propose a more convenient formulation to compute oxygen absorption.
    Keywords: CHEMISTRY
    Type: Journal of Geophysical Research; 79; Feb. 20
    Format: text
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